South Korean police said Thursday that North Korea may be responsible for renewed cyber attacks that have affected seven more Web sites.

South Korea's spy agency has identified the North with involvement in the initial cyber attacks that began Tuesday on South Korean and U.S. Web sites.

U.S. authorities also suspect North Korea as the origin of the trouble, but they warned it would be difficult to identify the attackers quickly.

North Korea has not responded to the accusations.

"The anticipated attack did take place, but considerable counter-measures were taken and it did act as a defense to some degree," an official at the online security firm Ahnlab said.

Though no major disruptions were reported, the National Cyber Security Center site in South Korea remains inaccessible.

"The damage from the latest attack appears to be limited because those sites took necessary measures to fend off the attack," said Ku Kyo-young, an official from the state-run Korea Communications Commission.

The White House, Pentagon, Treasury Department and the Nasdaq Stock Exchange were among some of the U.S targets.

The attacks also paralyzed Web sites in the U.S. over the Fourth of July holiday weekend.